Golf club grip and golf club

ABSTRACT

An object of the present disclosure is to provide a golf club grip comprising an inner layer that is hard to collapse and has excellent weather resistance. The present disclosure provides a golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 Nm or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree.

FIELD OF THE INVENTION

The present disclosure relates to a technology for improving an inner layer of a multiple layered golf club grip.

DESCRIPTION OF THE RELATED ART

As a grip attached to a golf club, a multiple layered grip is known. For example, JP 2016-093332 A discloses a grip for sporting goods comprising a cylindrical portion composed of a cylindrical inner layer and a cylindrical outer layer covering the inner layer, wherein the inner layer is a porous rubber layer or a porous resin layer, the outer layer is formed from a rubber composition containing an acrylonitrile-butadiene based rubber, and the acrylonitrile-butadiene based rubber includes a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber (hereinafter referred to as “HXNBR”).

JP 2017-113388 A discloses a grip for sporting goods comprising an outermost surface layer formed from a surface layer rubber composition, wherein the surface layer rubber composition contains (A) a base rubber and (B) a resin having a softening point in a range from 5° C. to 120° C., (A) the base rubber contains an acrylonitrile-butadiene based rubber, the acrylonitrile-butadiene based rubber includes a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber (hereinafter referred to as “HXNBR”), and (B) the resin incudes at least one member selected from the group consisting of a hydrogenated rosin ester, a disproportionated rosin ester, an ethylene-vinyl acetate copolymer, a coumarone resin, a phenol resin, a xylene resin and a styrene resin.

The grip for sporting goods disclosed in JP 2017-113388 A comprises a cylindrical portion composed of a cylindrical inner layer and a cylindrical outer layer covering the inner layer, a density (Din) of the inner layer is lower than a density (Dout) of the outer layer, and the density (Din) of the inner layer ranges from 0.20 g/cm³ to 0.50 g/cm³.

SUMMARY OF THE INVENTION

There is a problem that a multiple layered golf club grip, particularly a foamed inner layer is easy to collapse (easy to deform), and is easy to be degraded by ozone in the air. The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a golf club grip comprising an inner layer that is hard to collapse and has excellent weather resistance, and a golf club using the golf club grip.

The present disclosure that has solved the above problem provides a golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 N·m or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree.

According to the present disclosure, a golf club grip comprising an inner layer that is hard to collapse and has excellent weather resistance, and a golf club using the golf club grip are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one example of a golf club grip; FIG. 2 is a schematic cross-sectional view showing one example of a golf club grip; and

FIG. 3 is a perspective view showing one example of a golf club.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure provides a golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 N·m or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree. If the acrylonitrile-butadiene based rubber is used as the base rubber of the inner layer rubber composition, and the inner layer rubber composition has a maximum torque value of 0.5 N·m or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree, an inner layer that is hard to collapse and has excellent weather resistance is obtained.

The golf club grip according to the present disclosure comprises a cylindrical portion composed of a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer.

The cylindrical inner layer is formed from, for example, an inner layer rubber composition containing (A1) a base rubber. The cylindrical outer layer is formed from, for example, an outer layer rubber composition containing (A2) a base rubber. Each of the inner layer rubber composition and the outer layer rubber composition may further contain a resin, a crosslinking agent, a vulcanization accelerator, a vulcanization activator, a reinforcing material, an antioxidant, a softening agent, an anti-scorching agent, coloring agent, or the like.

First, the base rubber (A1, A2) contained in the inner layer rubber composition and the outer layer composition will be explained.

The inner layer rubber composition contains an acrylonitrile-butadiene based rubber as (A1) the base rubber. Examples of the acrylonitrile-butadiene based rubber include an acrylonitrile-butadiene rubber (NBR), a carboxyl-modified acrylonitrile-butadiene rubber (XNBR), a hydrogenated acrylonitrile-butadiene rubber (HNBR), and a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber (HXNBR).

The XNBR is a copolymer of a monomer having a carboxyl group, acrylonitrile and butadiene. The HNBR is a hydrogenated product of the acrylonitrile-butadiene rubber (NBR). The HXNBR is a hydrogenated product of the copolymer of the monomer having the carboxyl group, acrylonitrile and butadiene.

In the present disclosure, the acrylonitrile-butadiene based rubber used as (A1) the base rubber of the inner layer rubber composition preferably includes the acrylonitrile-butadiene rubber (NBR) and the hydrogenated acrylonitrile-butadiene rubber (HNBR).

In the acrylonitrile-butadiene rubber (NBR), the amount of acrylonitrile is preferably 10 mass % or more, more preferably 20 mass % or more, and even more preferably 30 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, and even more preferably 40 mass % or less. If the amount of acrylonitrile is 10 mass % or more, the adhesion to the outer layer material is better, and if the amount of acrylonitrile is 50 mass % or less, the processibility is not impaired.

The Mooney viscosity (ML₁₊₄ (100° C.)) of the acrylonitrile-butadiene rubber (NBR) is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, and is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. If the Mooney viscosity (ML₁₊₄ (100° C.)) falls within the above range, there is no problem in the processibility.

In the hydrogenated acrylonitrile-butadiene rubber (HNBR), the amount of acrylonitrile is preferably 10 mass % or more, more preferably 20 mass % or more, and even more preferably 30 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, and even more preferably 40 mass % or less. If the amount of acrylonitrile is 10 mass % or more, the adhesion to the outer layer material is better, and if the amount of acrylonitrile is 50 mass % or less, there is no problem in the processibility.

In the hydrogenated acrylonitrile-butadiene rubber (HNBR), the amount of the double bond is preferably 0.09 mmol/g or more, more preferably 0.2 mmol/g or more, and is preferably 2.5 mmol/g or less, more preferably 2.0 mmol/g or less, and even more preferably 1.5 mmol/g or less. If the amount of the double bond is 0.09 mmol/g or more, co-vulcanization of the blended NBR and sulfur becomes possible, and if the amount of the double bond is 2.5 mmol/g or less, the weather resistance is enhanced. The amount of the double bond is adjusted by the amount of butadiene in the copolymer or the amount of hydrogen added into the copolymer.

The Mooney viscosity (ML₁₊₄ (100° C.)) of the hydrogenated acrylonitrile-butadiene rubber (HNBR) is preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more, and is preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less. If the Mooney viscosity (ML₁₊₄ (100° C.)) falls within the above range, there is no problem in the processibility.

In the case that (A1) the base rubber includes the acrylonitrile-butadiene rubber (NBR) and the hydrogenated acrylonitrile-butadiene rubber (HNBR), the acrylonitrile-butadiene rubber (NBR) preferably has a greater Mooney viscosity (ML₁₊₄ (100° C.)) than the hydrogenated acrylonitrile-butadiene rubber (HNBR). If the acrylonitrile-butadiene rubber (NBR) has a greater Mooney viscosity (ML₁₊₄ (100° C.)) than the hydrogenated acrylonitrile-butadiene rubber (HNBR), when they are added, the improvement effect in the compression permanent strain is greater.

From this viewpoint, the difference (MV_(NBR)-MV_(HNBR)) between the Mooney viscosity (ML₁₊₄ (100° C.)) of the acrylonitrile-butadiene rubber (NBR) and the Mooney viscosity (ML₁₊₄ (100° C.)) of the hydrogenated acrylonitrile-butadiene rubber (HNBR) is preferably 1 or more, more preferably 10 or more, and is preferably 50 or less, more preferably 30 or less.

The amount of the acrylonitrile-butadiene based rubber in (A1) the base rubber is preferably 30 mass % or more, more preferably 40 mass % or more, and even more preferably 50 mass % or more. In addition, (A1) the base rubber of the inner layer rubber composition also preferably consists of the acrylonitrile-butadiene based rubber. It is noted that the amount of the acrylonitrile-butadiene based rubber in (A1) the base rubber is, for example, the total amount of the acrylonitrile-butadiene rubber (NBR) and the hydrogenated acrylonitrile-butadiene rubber (HNBR) in (A1) the base rubber when (A1) the base rubber includes the acrylonitrile-butadiene rubber (NBR) and the hydrogenated acrylonitrile-butadiene rubber (HNBR).

The amount of the acrylonitrile-butadiene rubber (NBR) in (A1) the base rubber is preferably 30 mass % or more, more preferably 40 mass % or more, and even more preferably 50 mass % or more, and is preferably 90 mass % or less, more preferably 80 mass % or less, and even more preferably 70 mass % or less. If the amount of the acrylonitrile-butadiene rubber (NBR) in (A1) the base rubber falls within the above range, a better balance between the compression permanent strain and the weather resistance is stricken.

Examples of (A2) the base rubber contained in the outer layer rubber composition include a natural rubber (NR), an ethylene-propylene-diene rubber (EPDM), a butyl rubber (IIR), an acrylonitrile-butadiene rubber (NBR), a hydrogenated acrylonitrile-butadiene rubber (HNBR), a carboxyl-modified acrylonitrile-butadiene rubber (XNBR), a butadiene rubber (BR), a styrene-butadiene rubber (SBR), a polyurethane rubber (PU), an isoprene rubber (IR), a chloroprene rubber (CR), and an ethylene-propylene rubber (EPM). These base rubbers may be used solely, or two or more of them may be used in combination.

The amount of (A2) the base rubber in the outer layer rubber composition is preferably 50 mass % or more, more preferably 55 mass % or more, and even more preferably 60 mass % or more.

(A2) The base rubber preferably includes the acrylonitrile-butadiene based rubber. The acrylonitrile-butadiene based rubber preferably includes at least one member selected from the group consisting of the acrylonitrile-butadiene rubber (NBR), the carboxyl-modified acrylonitrile-butadiene rubber (XNBR), the hydrogenated acrylonitrile-butadiene rubber (HNBR), and the carboxyl-modified hydrogenated acrylonitrile-butadiene rubber (HXNBR).

The amount of the acrylonitrile-butadiene based rubber in (A2) the base rubber is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more. In addition, (A2) the base rubber of the rubber composition also preferably consists of the acrylonitrile-butadiene based rubber.

The amount of acrylonitrile in the NBR, XNBR, HNBR and HXNBR is preferably 15 mass % or more, more preferably 18 mass % or more, and even more preferably 21 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, and even more preferably 40 mass % or less. If the amount of acrylonitrile is 15 mass % or more, the abrasion resistance is better, and if the amount of acrylonitrile is 50 mass % or less, the grip has a better touch feeling in a cold region or in winter.

The amount of the double bond in the HNBR and HXNBR is preferably 0.09 mmol/g or more, more preferably 0.2 mmol/g or more, and is preferably 2.5 mmol/g or less, more preferably 2.0 mmol/g or less, and even more preferably 1.5 mmol/g or less. If the amount of the double bond is 0.09 mmol/g or more, vulcanization is easily carried out during molding and the grip has enhanced tensile strength, and if the amount of the double bond is 2.5 mmol/g or less, the grip has better durability (weather resistance) and tensile strength. The amount of the double bond is adjusted by the amount of butadiene in the copolymer or the amount of hydrogen added into the copolymer.

The monomer having the carboxyl group in the XNBR and HXNBR include acrylic acid, methacrylic acid, fumaric acid, and maleic acid. The amount of the monomer having the carboxyl group in the XNBR and HXNBR is preferably 1.0 mass % or more, more preferably 2.0 mass % or more, and even more preferably 3.5 mass % or more, and is preferably 30 mass % or less, more preferably 25 mass % or less, and even more preferably 20 mass % or less. If the amount of the monomer having the carboxyl group is 1.0 mass % or more, the abrasion resistance is better, and if the amount of the monomer having the carboxyl group is 30 mass % or less, the grip has a better touch feeling in a cold region or in winter.

The amount of the carboxyl group in the XNBR and HXNBR is preferably 1.0 mass % or more, more preferably 2.0 mass % or more, and even more preferably 3.5 mass % or more, and is preferably 30 mass % or less, more preferably 25 mass % or less, and even more preferably 20 mass % or less. If the amount of the carboxyl group is 1.0 mass % or more, the abrasion resistance is better, and if the amount of the carboxyl group is 30 mass % or less, the grip has a better touch feeling in a cold region or in winter.

(A2) The base rubber preferably includes at least one member selected from the group consisting of the XNBR, HNBR and HXNBR, and particularly preferably includes HXNBR. In other words, the outer layer preferably contains at least one member selected from the group consisting of the carboxyl-modified acrylonitrile-butadiene rubber (XNBR), the hydrogenated acrylonitrile-butadiene rubber (HNBR), and the carboxyl-modified hydrogenated acrylonitrile-butadiene rubber (HXNBR), more preferably contains the HXNBR. If the base rubber of the outer layer includes the above rubber, the grip has enhanced abrasion resistance and weather resistance.

The Mooney viscosity (ML₁₊₄ (100° C.)) of the HXNBR is preferably 60 or more, more preferably 64 or more, and even more preferably 68 or more, and is preferably 95 or less, more preferably 90 or less, and even more preferably 85 or less. If the Mooney viscosity (ML₁₊₄ (100° C.)) is 60 or more, the grip has further enhanced abrasion resistance, and if the Mooney viscosity (ML₁₊₄ (100° C.)) is 95 or less, the rubber composition has better processibility.

Next, the components that can be contained in each of the inner layer rubber composition and the outer layer rubber composition will be explained. Unless stated otherwise, the preferable amount of each component is an amount with respect to (A1, A2) the base rubber contained in the inner layer rubber composition or the outer layer rubber composition, respectively.

(B) Resin

Each of the inner layer rubber composition and the outer layer rubber composition can further contain (B) a resin. (B) The resin is a component that lowers the Mooney viscosity of the inner layer rubber composition and the outer layer rubber composition. Examples of (B) the resin include a rosin ester, an ethylene-vinyl acetate copolymer, a coumarone resin, and a phenol resin.

The amount of (B) the resin is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, and is preferably 45 parts by mass or less, more preferably 42 parts by mass or less, and even more preferably 40 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber. If the amount of (B) the resin is 5 parts by mass or more, the grip has better feeling, and if the amount of (B) the resin is 45 parts by mass or less, the grip has further enhanced abrasion resistance.

The amount of vinyl acetate in (B1) the ethylene-vinyl acetate copolymer is preferably 10 mass % or more, more preferably 12 mass % or more, and even more preferably 15 mass % or more, and is preferably 80 mass % or less, more preferably 75 mass % or less, and even more preferably 70 mass % or less. If the amount of vinyl acetate is 10 mass % or more, the grip has better feeling, and if the amount of vinyl acetate is 80 mass % or less, the grip has further enhanced abrasion resistance.

The Mooney viscosity (ML₁₊₄ (100° C.)) of (B1) the ethylene-vinyl acetate copolymer is preferably 20 or more, more preferably 23 or more, and even more preferably 25 or more, and is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. If the Mooney viscosity (ML₁₊₄ (100° C.)) is 20 or more, the rubber composition has better processibility, and if the Mooney viscosity (ML₁₊₄ (100° C.)) is 50 or less, the grip has better feeling.

The amount of (B1) the ethylene-vinyl acetate copolymer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, and is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber. If the amount of (B1) the ethylene-vinyl acetate copolymer is 3 parts by mass or more, the grip has better feeling, and if the amount of (B1) the ethylene-vinyl acetate copolymer is 40 parts by mass or less, the grip has further enhanced abrasion resistance.

(B2) The rosin ester is an ester compound obtained by a reaction between a rosin and an alcohol. The rosin is a natural resin containing abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, and dehydroabietic acid. Examples of the alcohol include a monohydric alcohol such as n-octyl alcohol, 2-ethylhexyl alcohol, decyl alcohol, lauryl alcohol and stearyl alcohol; a dihydric alcohol such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol and neopentyl glycol; a trihydric alcohol such as glycerin and trimethylolpropane; a tetrahydric alcohol such as pentaerythritol and diglycerin; and a hexahydric alcohol such as dipentaerythritol and sorbitol. Among them, the polyhydric alcohol such as the dihydric alcohol or higher alcohol is preferable, and glycerin is more preferable.

Examples of the rosin ester include a hydrogenated rosin ester and a disproportionated rosin ester. The hydrogenated rosin ester and the disproportionated rosin ester are so-called stabilized rosin esters.

The hydrogenated rosin ester is an ester compound having the moiety derived from the rosin of the rosin ester and the moiety is hydrogenated. The hydrogenated rosin ester may be obtained by a method of hydrogenating the rosin followed by carrying out a reaction between the obtained hydrogenated rosin and an alcohol, or a method of carrying out a reaction between the rosin and an alcohol followed by hydrogenating the obtained rosin ester.

The disproportionated rosin ester is an ester compound having the moiety derived from the rosin of the rosin ester and the moiety is disproportionated. The disproportionated rosin ester may be obtained by a method of disproportionating the rosin followed by carrying out a reaction between the obtained disproportionated rosin and an alcohol, or a method of carrying out a reaction between the rosin and an alcohol followed by disproportionating the obtained rosin ester.

The acid value of the rosin ester is preferably 2 mgKOH/g or more, more preferably 4 mgKOH/g or more, and even more preferably 6 mgKOH/g or more, and is preferably 200 mgKOH/g or less, more preferably 180 mgKOH/g or less, and even more preferably 160 mgKOH/g or less. If the acid value is 2 mgKOH/g or more, the rosin ester has better compatibility with the acrylonitrile-butadiene based rubber, and if the acid value is 200 mgKOH/g or less, the carboxyl group of the rosin ester nearly has no effect on the vulcanization reaction of the base rubber.

The amount of (B2) the rosin ester is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, and is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber. If the amount of (B2) the rosin ester is 2 parts by mass or more, the rubber composition is more flexible, and if the amount of (B2) the rosin ester is 15 parts by mass or less, the rubber composition has better processibility.

The coumarone resin is a resin comprising a coumarone-based compound as the monomer component. As the coumarone resin, a coumarone⋅indene resin is preferable. The coumarone⋅indene resin is a copolymer comprising the coumarone-based compound and an indene-based compound as the monomer component in a total amount of 50 mass % or more in all the monomer components. Examples of the coumarone-based compound include coumarone and methylcoumarone. The amount of the coumarone-based compound in all the monomer components preferably ranges from 1 mass % to 20 mass %. Examples of the indene-based compound include indene and methylindene. The amount of the indene-based compound in all the monomer components preferably ranges from 40 mass % to 95 mass %. The coumarone⋅indene resin may further comprise other monomer components than the coumarone-based compound and the indene-based compound. Examples of the other monomer components include styrene, vinyltoluene, and dicyclopentadiene.

Examples of the phenol resin include a condensation product of a phenol-based compound and formaldehyde. Examples of the phenol-based compound include phenol and m-cresol. In addition, the phenol resin includes a resol obtained by an addition reaction between the phenol-based compound and formaldehyde with an alkali catalyst; and a novolac obtained by a condensation reaction between the phenol-based compound and formaldehyde with an acid catalyst. Further, the phenol resin also includes a rosin phenol resin obtained by an addition and thermopolymerization reaction between a rosin and the phenol-based compound with an acid catalyst.

The inner layer rubber composition preferably contains (B2) the rosin ester as (B) the resin.

The outer layer rubber composition preferably contains (B1) the ethylene-vinyl acetate copolymer and (B2) the rosin ester as (B) the resin. If (B1) the ethylene-vinyl acetate copolymer and (B2) the rosin ester are contained, they melt during processing and the rubber composition becomes soft, thus the stress at deformation is lowered.

In the case that the outer layer rubber composition contains (B1) the ethylene-vinyl acetate copolymer and (B2) the rosin ester, the mass ratio (B1/B2) of (B1) the ethylene-vinyl acetate copolymer to (B2) the rosin ester is preferably 0.8 or more, more preferably 1.0 or more, even more preferably 1.2 or more, and most particularly preferably 1.5 or more, and is preferably 5.0 or less, more preferably 4.8 or less, and even more preferably 4.5 or less.

In the case that the outer layer rubber composition contains (B1) the ethylene-vinyl acetate copolymer and (B2) the rosin ester, the total amount (B1+B2) of (B1) the ethylene-vinyl acetate copolymer and (B2) the rosin ester is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, and is preferably 45 parts by mass or less, more preferably 42 parts by mass or less, and even more preferably 40 parts by mass or less, with respect to 100 parts by mass of (A2) the base rubber.

(C) Crosslinking agent

The inner layer rubber composition and the outer layer rubber composition preferably contain a crosslinking agent for crosslinking the base rubber. As the crosslinking agent, a sulfur crosslinking agent and an organic peroxide can be used. Examples of the sulfur crosslinking agent include an elemental sulfur and a sulfur donor type compound. Examples of the elemental sulfur include powdery sulfur, precipitated sulfur, colloidal sulfur, and insoluble sulfur. Examples of the sulfur donor type compound include 4,4′-dithiobismorpholine. Examples of the organic peroxide include dicumyl peroxide, α,α′-bis(t-butylperoxy-m-diisopropyl) benzene, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, and 1,1-bis(t-butylperoxy)-3,3, 5-trimethylcyclohexane. The crosslinking agent may be used solely, or two or more of them may be used in combination. As the crosslinking agent, the sulfur crosslinking agent is preferred, and the elemental sulfur is more preferred.

The amount of the crosslinking agent is preferably 0.2 part by mass or more, more preferably 0.4 part by mass or more, and even more preferably 0.6 part by mass or more, and is preferably 4.0 parts by mass or less, more preferably 3.5 parts by mass or less, and even more preferably 3.0 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber.

The inner layer rubber composition and the outer layer rubber composition preferably further contain a vulcanization accelerator or a vulcanization activator.

(D) Vulcanization accelerator

Examples of the vulcanization accelerator include thiurams such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram monosulfide (TMTM), dipentamethylenethiuram tetrasulfide and tetrakis(2-ethylhexyl)thiuram disulfide; guanidines such as diphenylguanidine (DPG); dithiocarbamates such as zinc dimethyldithiocarbamate (ZnPDC), and zinc dibutyldithiocarbamate; thioureas such as trimethylthiourea, and N,N′-diethylthiourea; thiazoles such as mercaptobenzothiazole (MBT), and benzothiazole disulfide; and sulfenamides such as N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N-t-butyl-2-benzothiazolylsulfenamide (BBS). These vulcanization accelerators may be used solely, or two or more of them may be used in combination.

The total amount of the vulcanization accelerator is preferably 0.4 part by mass or more, more preferably 0.8 part by mass or more, and even more preferably 1.2 parts by mass or more, and is preferably 9.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 7.0 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber.

(E) Vulcanization activator

Examples of the vulcanization activator include a metal oxide, a metal peroxide, and a fatty acid. Examples of the metal oxide include zinc oxide, magnesium oxide, and lead oxide. Examples of the metal peroxide include zinc peroxide, chrome peroxide, magnesium peroxide, and calcium peroxide. Examples of the fatty acid include stearic acid, oleic acid, and palmitic acid. These vulcanization activators may be used solely, or two or more of them may be used in combination.

The total amount of the vulcanization activator is preferably 0.5 part by mass or more, more preferably 0.6 part by mass or more, and even more preferably 0.7 part by mass or more, and is preferably 10.0 parts by mass or less, more preferably 9.5 parts by mass or less, and even more preferably 9.0 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber.

The inner layer rubber composition and the outer layer rubber composition may further contain a reinforcing material, an antioxidant, a softening agent, an anti-scorching agent, a coloring agent, or the like, where necessary.

Examples of the reinforcing material include carbon black and silica. The amount of the reinforcing material is preferably 2.0 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 4.0 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber.

Examples of the antioxidant include imidazoles, amines, phenols and thioureas. Examples of the imidazoles include nickel dibutyldithiocarbamate (NDIBC), 2-mercaptobenzim idazole, and zinc salt of 2-mercaptobenzim idazole. Examples of the amines include phenyl-α-naphtylamine. Examples of the phenols include 2,2′-methylene bis(4-methyl-6-t-butylphenol) (MBMBP), and 2,6-di-tert-butyl-4-methylphenol. Examples of the thioureas include tributyl thiourea, and 1,3-bis(dimethylaminopropyl)-2-thiourea. These antioxidants may be used solely, or two or more of them may be used in combination.

The amount of the antioxidant is preferably 0.2 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.4 part by mass or more, and is preferably 5.0 parts by mass or less, more preferably 4.8 parts by mass or less, and even more preferably 4.6 parts by mass or less, with respect to 100 parts by mass of (A1, A2) the base rubber.

Examples of the softening agent include a mineral oil and a plasticizer. Examples of the mineral oil include paraffin oil, naphthene oil, and aromatic oil. Examples of the plasticizer include dioctyl phthalate, dibutyl phthalate, dioctyl sebacate, and dioctyl adipate.

Examples of the anti-scorching agent include an organic acid and a nitroso compound. Examples of the organic acid include phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, benzoic acid, salicylic acid, and malic acid. Examples of the nitroso compound include N-nitrosodiphenylamine, N-(cyclohexylthio)phthalimide, sulfonamide derivative, diphenyl urea, bis(tridecyl)pentaerythritol diphosphite, and 2-mercaptobenzim idazole.

Each of the inner layer and the outer layer may be a solid layer or a porous layer. If the inner layer or outer layer is the porous layer, the golf club grip has a light weight. The porous layer is a layer having a plurality of fine pores (voids) formed in the rubber which is the base material. If a plurality of fine pores are formed, the layer has a low apparent density, and thus the golf club grip has a light weight.

Examples of the method producing the porous layer include a balloon foaming method, chemical foaming method, supercritical carbon dioxide injection molding method, salt extraction method, and solvent removing method. In the balloon foaming method, microballoons are allowed to be contained in the rubber composition, and then be expanded by heating to perform foaming. In addition, the expanded microballoons may be blended in the rubber composition, and then the resultant rubber composition is molded. In the chemical foaming method, a foaming agent (such as azodicarbonamide, azobisisobutyronitrile, N,N′-dinitrosopentamethylenetetramine, p-toluenesulfonyl hydrazine, and p-oxybis(benzenesulfonohydrazide)) and a foaming auxiliary are allowed to be contained in the rubber composition, and then a gas (such as carbon dioxide gas and nitrogen gas) is generated by a chemical reaction to perform foaming. In the supercritical carbon dioxide injection molding method, the rubber composition is immersed in carbon dioxide being in a supercritical state at a high pressure, the resultant rubber composition is injected at a normal pressure, and carbon dioxide is gasified to perform foaming. In the salt extraction method, a soluble salt (such as boric acid and calcium chloride) is allowed to be contained in the rubber composition, and then the salt is dissolved and extracted after molding to form fine pores. In the solvent removing method, a solvent is allowed to be contained in the rubber composition, and then the solvent is removed after molding to form fine pores.

When the inner layer or outer layer is the porous layer, a foamed layer formed from a rubber composition containing a foaming agent is preferred. In particular, a foamed layer formed by the balloon foaming method is preferred.

As the microballoons, organic microballoons or inorganic microballoons may be used. Examples of the organic microballoons include hollow particles formed from a thermoplastic resin, and resin capsules encapsulating a hydrocarbon having a low boiling point in a shell formed from a thermoplastic resin. Specific examples of the resin capsules include Expancel (registered trademark) manufactured by Akzo Nobel Company, and Matsumoto Microsphere (registered trademark) manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Examples of the inorganic microballoons include hollow glass particles (such as silica balloons and alumina balloons), and hollow ceramic particles.

The volume average particle size of the resin capsule (before expansion) is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 9 μm or more, and is preferably 90 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less.

The inner layer is preferably the porous layer, more preferably the foamed layer formed by the balloon foaming method. When the inner layer is produced by the balloon foaming method, the amount of the microballoons in the inner composition is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 15 parts by mass or less, with respect to 100 parts by mass of the base rubber. If the amount of the microballoons is 5 parts by mass or more, the effect of reducing the weight of the grip becomes greater, and if the amount of the microballoons is 20 parts by mass or less, lowering in the mechanical strength of the inner layer is suppressed.

In addition, the foaming ratio of the inner layer prepared by the balloon foaming method is preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 1.8 or more, and is preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. If the foaming ratio is 1.2 or more, the effect of reducing the weight of the grip becomes greater, and if the foaming ratio is 5.0 or less, lowering in the mechanical strength of the inner layer is suppressed.

When the outer layer is produced by the balloon foaming method, the amount of the microballoons in the outer rubber composition is preferably 1.0 part by mass or more, more preferably 1.2 parts by mass or more, and even more preferably 1.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, with respect to 100 parts by mass of the base rubber. If the amount of the microballoons is 1.0 part by mass or more, foaming can be performed more uniformly at the time of forming the porous layer, and if the amount of the microballoons is 10 parts by mass or less, the porous layer strikes a good balance between the light weight and the mechanical strength.

The material hardness (Shore A hardness) of the inner layer rubber composition is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, and is preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. If the material hardness (Shore A hardness) of the inner layer rubber composition is 30 or more, the inner layer does not become excessively soft and thus a tightly fixed touch feeling is obtained when holding the grip, and if the material hardness (Shore A hardness) of the inner layer rubber composition is 60 or less, the inner layer does not become excessively hard and thus the grip feeling when holding the grip becomes better.

In the present disclosure, the inner layer rubber composition preferably has the maximum torque value of 0.5 Nm or more, more preferably 0.6 Nm or more, and even more preferably 0.7 Nm or more, and preferably has the maximum torque value of 1.3 Nm or less, more preferably 1.2 Nm or less, and even more preferably 1.1 Nm or less in a vulcanization curve measured at the temperature of 165° C. and the amplitude angle of one degree. The maximum torque value indicates vulcanization characteristics of the double bond included in the inner layer rubber composition. If the maximum torque value in the vulcanization curve measured at the temperature of 165° C. and the amplitude angle of one degree is 0.5 Nm or more, the obtained grip is hard to collapse during using. In addition, if the maximum torque value in the vulcanization curve measured at the temperature of 165° C. and the amplitude angle of one degree is 1.3 Nm or less, bad foaming is hard to occur.

The Mooney viscosity (ML₁₊₄ (100° C.)) of the inner layer rubber composition is preferably 35 or more, more preferably 37 or more, and even more preferably 39 or more, and is preferably 55 or less, more preferably 53 or less, and even more preferably 50 or less. If the Mooney viscosity (ML₁₊₄ (100° C.)) falls within the above range, the inner layer rubber composition has better processibility.

The material hardness (Shore A hardness) of the outer layer rubber composition is preferably 25 or more, more preferably 28 or more, and even more preferably 30 or more, and is preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. If the material hardness (Shore A hardness) of the outer layer rubber composition is 25 or more, the outer layer has further enhanced mechanical strength, and if the material hardness (Shore A hardness) of the outer layer rubber composition is 60 or less, the outer layer does not become excessively hard, and thus the grip feeling when holding the grip becomes better.

[Production method of grip]

The inner layer rubber composition and the outer layer rubber composition can be prepared by a conventional method, for example, by kneading materials with a kneading machine such as a Banbury mixer, a kneader, and an open roll. It is noted that when the inner layer rubber composition or the outer layer rubber composition contains microballoons, the components other than the microballoons are preferably kneaded in advance followed by kneading the kneaded mixture and the microballoons. The material temperature during kneading the kneaded mixture and the microballoons is preferably lower than the expansion starting temperature of the microballoons.

The golf club grip may be obtained by molding the inner layer rubber composition or outer layer rubber composition in a mold. Examples of the molding method include a press molding method and an injection molding method. The golf club grip having the inner layer and the outer layer may be obtained, for example, by press molding a laminated product composed of an unvulcanized rubber sheet formed from the outer layer rubber composition and an unvulcanized rubber sheet formed from the inner layer rubber composition in a mold. When the press molding method is adopted, the temperature of the mold preferably ranges from 140° C. to 200° C., the molding time preferably ranges from 5 minutes to 40 minutes, and the molding press preferably ranges from 0.1 MPa to 100 MPa.

[Construction of grip]

The golf club grip according to the present disclosure comprises the cylindrical portion composed of the cylindrical inner layer and the cylindrical outer layer provided outside the inner layer. The cylindrical portion has at least a dual layered construction having the inner layer and the outer layer. The cylindrical portion may have, for example, a dual layered construction composed of a single layered inner layer and a single layered outer layer, or a triple layered construction composed of a dual layered inner layer and a single layered outer layer. The golf club grip according to the present disclosure preferably comprises the dual layered cylindrical portion composed of the cylindrical inner layer and the outer layer covering the inner layer.

Examples of the combination of the outer layer and the inner layer include a combination of a solid outer layer and a solid inner layer, a combination of a solid outer layer and a porous inner layer, and a combination of a porous outer layer and a porous inner layer. Among them, the combination of the solid outer layer and the porous inner layer, and the combination of the porous outer layer and the porous inner layer are preferable. According to the present disclosure, an inner layer having good mechanical strength without collapsing is obtained even if the inner layer is porous.

The thickness of the cylindrical portion is preferably 0.5 mm or more, more preferably 1.0 mm or more, even more preferably 1.5 mm or more, and is preferably 17.0 mm or less, more preferably 10.0 mm or less, even more preferably 8.0 mm or less. The cylindrical portion may be formed with a fixed thickness along the axis direction, or may be formed with a thickness gradually becoming thicker from the front end toward the back end.

The outer layer and the inner layer may have a uniform thickness, or may have a varied thickness. For example, the outer layer and the inner layer may be formed with a thickness gradually becoming thicker from one end toward another end along the axis direction of the cylindrical grip. The outer layer preferably has a uniform thickness.

When the cylindrical portion has a thickness in a range of from 0.5 mm to 17.0 mm, the thickness of the outer layer is preferably 0.5 mm or more, more preferably 0.6 mm or more, and even more preferably 0.7 mm or more, and is preferably 2.5 mm or less, more preferably 2.3 mm or less, and even more preferably 2.1 mm or less. If the thickness of the outer layer is 0.5 mm or more, the reinforcing effect by the outer layer material becomes greater, and if the thickness of the outer layer is 2.5 mm or less, the inner layer is relatively thickened and thus the effect of reducing the weight of the grip becomes greater.

The percentage ((thickness of outer layer/thickness of cylindrical portion)×100) of the thickness of outer layer to the thickness of cylindrical portion is preferably 0.5% or more, more preferably 1.0% or more, and even more preferably 1.5% or more, and is preferably 99.0% or less, more preferably 98.0% or less, and even more preferably 97.0% or less. If the percentage is 0.5% or more, the reinforcing effect by the outer layer material becomes greater, and if the percentage is 99.0% or less, the inner layer is relatively thickened and thus the effect of reducing the weight of the grip becomes greater.

The elongation at break of the inner layer in a tensile test is preferably 730% or less, more preferably 710% or less, and even more preferably 690% or less, and is preferably 300% or more, more preferably 350% or more, and even more preferably 400% or more. If the elongation at break of the inner layer in the tensile test is 730% or less, collapsing is suppressed and sufficient crosslinking density is obtained. In addition, if the elongation at break of the inner layer in the tensile test is 300% or more, the inner layer is hardly broken when inserting the shaft into the grip.

The swollen ratio of the inner layer in a toluene swollen test is preferably 200% or less, more preferably 180% or less, and even more preferably 160% or less, and is preferably 100% or more, more preferably 110% or more, and even more preferably 120% or more. If the swollen ratio of the inner layer in the toluene swollen test is 200% or less, collapsing is suppressed and sufficient crosslinking density is obtained. In addition, if the swollen ratio of the inner layer in the toluene swollen test is 100% or more, the solvent used for inserting the shaft is absorbed by the grip, and thus the adhesion between the grip and the shaft is better.

When the inner layer is porous, the density (Din) of the inner layer is preferably 0.20 g/cm³ or more, more preferably 0.22 g/cm³ or more, and even more preferably 0.25 g/cm³ or more, and is preferably 0.6 g/cm³ or less, more preferably 0.55 g/cm³ or less, and even more preferably 0.5 g/cm³ or less. If the density of the inner layer is 0.20 g/cm³ or more, the inner layer does not excessively deform and thus a stronger hitting feeling is obtained, and if the density of the inner layer is 0.6 g/cm³ or less, the effect of reducing the weight of the grip by the porous layer is greater.

Examples of the shape of the golf club grip include a shape having a cylindrical portion for inserting a shaft, and an integrally molded cap portion for covering the opening of the back end of the cylindrical portion. Further, the cylindrical portion has a laminated construction composed of the inner layer and the outer layer. In addition, the cylindrical portion and the cap portion may be formed separately, and then adhered together.

The cylindrical portion may be formed with a fixed thickness along the axis direction, or may be formed with a thickness gradually becoming thicker from the front end toward the back end. In addition, the cylindrical portion may be formed with a fixed thickness along the diameter direction, or a projecting strip portion (so-called back line) may be formed on a part of the cylindrical portion. Furthermore, grooves may be formed on the surface of the cylindrical portion. Formation of a water film between the hand of the golfer and the grip may be suppressed by the grooves, and thus the grip performance under a wet condition is further enhanced. In addition, in view of the anti-slipping performance and abrasion resistance of the grip, a reinforcing cord may be disposed in the grip.

The mass of the golf club grip is preferably 16 g or more, more preferably 18 g or more, and even more preferably 20 g or more, and is preferably 35 g or less, more preferably 32 g or less, and even more preferably 30 g or less.

[Golf club]

The present disclosure also includes a golf club using the above golf club grip. The golf club comprises a shaft, a head provided on one end of the shaft, and a grip provided on another end of the shaft, wherein the grip is the golf club grip according to the present disclosure. The shaft can be made of stainless steel or a carbon fiber reinforced resin. Examples of the head include a wood type, a utility type, and an iron type. The material constituting the head is not particularly limited, and examples thereof include titanium, titanium alloy, carbon fiber reinforced plastic, stainless steel, maraging steel and soft iron.

Next, the golf club grip and the golf club will be explained with reference to figures. FIG. 1 is a perspective view showing one example of a golf club grip. A grip 1 has a cylindrical portion 2 for inserting a shaft, and an integrally molded cap portion 3 for covering the opening of the back end of the cylindrical portion.

FIG. 2 is a schematic cross-sectional view showing one example of a golf club grip. A cylindrical portion 2 is composed of an inner layer 2 a and an outer layer 2 b. The outer layer 2 b is formed with a uniform thickness throughout the entire region from the front end to the back end. The inner layer 2 a is formed with a thickness gradually becoming thicker from the front end toward the back end. In the grip 1 shown in FIG. 2 , the cap portion 3 is formed from the same rubber composition as the outer layer 2 b.

FIG. 3 is a perspective view showing one example of the golf club according to the present disclosure. A golf club 4 comprises a shaft 5, a head 6 provided on one end of the shaft 5, and a grip 1 provided on another end of the shaft 5. The back end of the shaft 5 is inserted into the cylindrical portion 2 of the grip 1.

EXAMPLES

Next, the present disclosure will be described in detail by way of examples. However, the present disclosure is not limited to the examples described below. Various changes and modifications without departing from the spirit of the present disclosure are included in the scope of the present disclosure.

[Evaluation method]

(1) Amount of acrylonitrile

The amount of acrylonitrile in the acrylonitrile-butadiene rubber before hydrogenation was measured according to ISO 24698-1 (2008).

(2) Amount of double bond (mmol/g)

The amount of the double bond is calculated from the amount (mass %) of butadiene in the copolymer and the amount (%) of a residual double bond. The amount of the residual double bond is a mass ratio (amount of the double bond after hydrogenation/amount of the double bond before hydrogenation) of the double bond in the copolymer after hydrogenation to the double bond in the copolymer before hydrogenation, and can be measured by infrared spectroscopy. In the case that the acrylonitrile-butadiene rubber is an acrylonitrile-butadiene binary copolymer, the amount of butadiene in the copolymer is calculated by subtracting the amount (mass %) of acrylonitrile from 100.

Amount of double bond={amount of butadiene/54}×amount of residual double bond×10

(3) Mooney viscosity (ML₁₊₄ (100° C.))

The Mooney viscosity of the rubber composition was measured according to JIS K6300-1 (2013). The measurement was carried out using an L-shaped rotor.

(4) Material hardness (Shore A hardness)

A sheet with a thickness of about 2 mm was produced by pressing the rubber composition at a temperature of 160° C. for 8 to 20 minutes. It is noted that when the rubber composition contains microballoons, the sheet was formed by expanding the microballoons in the same foaming ratio as that when forming the grip. The sheet was stored at a temperature of 23° C. for two weeks. At least three of these sheets were stacked on one another so as not to be affected by the measuring substrate on which the sheets were placed, and the hardness of the stack was measured with an automatic hardness tester (Digitest II, available from Bareiss company) using a testing device of “Shore A”.

(5) Tensile elongation at break (EB)

The tensile elongation at break was measured according to JIS K 6251 (2017). Specifically, a sheet with a thickness of 1 mm was produced by pressing the inner layer rubber composition at a temperature of 160° C. for 8 to 20 minutes. It is noted that when the inner layer rubber composition contains microballoons, the sheet was produced by expanding the microballoons in the same foaming ratio as that when forming the grip. The sheet was punched into a dumbbell shape (Dumbbell shape No. 3) to prepare a test piece, and the properties of the test piece were measured (measurement temperature: 23° C., tensile speed: 500 mm/min) with a tensile test measurement apparatus (Autograph AGS-D available from Shimadzu Corporation). The elongation at the time when the test piece was broken was recorded.

(6) Vulcanization characteristic test

The vulcanization curve was measured with CURELASTOMETER (registered trademark) at a temperature of 165° C. and an amplitude angle of one degree according to JIS K6300-2 “Rubber, unvulcanized—Physical properties—Part 2: Determination of vulcanization characteristics using an oscillating curemeter”, and the maximum torque value (Nm) was determined from the vulcanization curve.

(7) Toluene swollen ratio (%)

A sheet with a thickness of 1 mm was produced by pressing the inner layer rubber composition at a temperature of 160° C. for 8 to 20 minutes. It is noted that when the inner layer rubber composition contains microballoons, the sheet was produced by expanding the microballoons in the same foaming ratio as that when forming the grip. A square test piece with a side length of 2 mm was cut from the sheet with the thickness of 1 mm. The test piece was immersed in toluene at a temperature of 40° C. for 22 hours. Based on the volumes of the test piece before and after the immersion, the toluene swollen ratio (%) was calculated according to the following formula.

Toluene swollen ratio (%)=100×(V2−V1)/V1

V2: volume of the test piece after the toluene immersion, V1: volume of the test piece before the toluene immersion

(8) Compression permanent strain

A test piece with a diameter of 29 mm and a thickness of 12.5 mm was produced by pressing the inner layer rubber composition at a temperature of 160° C. for 8 to 20 minutes. It is noted that when the inner layer rubber composition contains microballoons, the sheet was produced by expanding the microballoons in the same foaming ratio as that when forming the grip. The test piece was compressed by 25% at a temperature of 25° C., and placed for 22 hours. The thickness (t0) of the test piece before the test, and the thickness (t2) of the test piece 30 minutes later after the test (placed for 22 hours) were measured, and the compression permanent strain was calculated according to the following formula.

ti Compression permanent strain (CS)=(t0-t2)/(t0-t1)×100

-   -   t0: thickness of the test piece before the compression     -   t2: thickness of the test piece 30 minutes later after the test     -   t1: thickness of the spacer controlling the compression ratio         (9.38 mm)

(9) Collapsing of grip

A durability test of 3000 times (actual hitting test by human) was conducted with a driver, and the durability was evaluated according to the following standard.

-   -   1: there is collapsing over the whole grip.     -   2: there is collapsing in the bat portion and the portion where         the right thumb grips.     -   3: there is collapsing in the bat portion.     -   4: there is no collapsing.

(10) Evaluation of weather resistance

A test piece comprising the inner layer and the outer layer was prepared from the grip. The prepared test piece was elongated by 10%, and placed in an environment of an ozone concentration of 50 pphm and a temperature of 40° C. for 24 hours. The test piece (inner layer) after the test was visually observed, and the weather resistance thereof was evaluated according to the following standard.

-   -   1: there are deep fractures.     -   2: there are many shallow fractures.     -   3: there are a few shallow fractures.     -   4: there are no fractures.

[Production of grip]

According to the formulations shown in Tables 1 and 2, the materials were kneaded to prepare the outer layer rubber compositions and the inner layer rubber compositions. It is noted that, the outer layer rubber compositions were prepared by kneading all the materials with a Banbury mixer, and the inner layer rubber compositions were prepared by kneading the materials except the microballoons with a Banbury mixer followed by blending the microballoons therein with a roll. The material temperature when kneading the inner layer rubber compositions with the Banbury mixer and the material temperature when blending the microballoons with the roll is lower than the expansion starting temperature of the microballoons.

TABLE 1 Outer layer rubber composition No. A Outer (A2) Base rubber HXNBR 100 layer (B) Resin EVA 30 Sylvatac RE 5S 8 Reinforcing material SEAST 3 5 Vulcanization activator Struktol ZP 1014 5 Crosslinking agent Sulfur 1.5 Vulcanization accelerator Sanceller TB_(Z)TD 1 Nocceler TOT-N 1 Nocceler EUR 1 Formulation: parts by mass

TABLE 2 Inner layer rubber composition No. a b c d e f g h i j k Inner (A1) Base rubber HNBR (CN amount: 34%, MV: 39) 100 — — — 70 50 30 50 70 50 30 layer NBR-1 (CN amount: 18%, MV: 33) — 100 — — 30 50 70 — — — — NBR-2 (CN amount: 26%, MV: 56) — — 100 — — — — 50 — — — NBR-3 (CN amount: 34%, MV: 45) — — — 100 — — — — 30 50 70 (B) Resin Sylvatac RE 5S 10 10 10 10 10 10 10 10 10 10 10 Reinforcing material SEAST 3 20 20 20 20 20 20 20 20 20 20 20 Vulcanization activator Zinc oxide 3 3 3 3 3 3 3 3 3 3 3 Crosslinking agent Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization accelerator Nocceler TOT-N 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Foaming agent Microballoons 10 10 10 10 10 10 10 10 10 10 10 Formulation: parts by mass

Materials used in Tables 1 and 2 are shown below.

HXNBR: hydrogenated carboxyl-modified acrylonitrile-butadiene rubber (Therban XT VPKA 8889 (amount of residual double bond: 3.5%, amount of acrylonitrile: 33.0 mass %, amount of double bond: 0.40 mmol/g, amount of carboxyl group-containing monomer: 5.0 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 77) available from ARANXEO Corporation)

HNBR: hydrogenated acrylonitrile-butadiene rubber (Therban AT3443VP (amount of residual double bond: 4%, amount of acrylonitrile: 34 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 39) available from ARANXEO Corporation)

NBR1: Nipol DN401 LL (amount of acrylonitrile: 18 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 33) available from Zeon Corporation

NBR2: N240S (amount of acrylonitrile: 26 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 56) available from JSR Corporation

NBR3: N231L (amount of acrylonitrile: 34 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 45) available from JSR Corporation

EVA: ethylene-vinyl acetate copolymer (Levapren 500 (amount of vinyl acetate: 50 mass %, Mooney viscosity (ML₁₊₄ (100° C.): 27) available from ARANXEO Corporation)

Sylvatac RE 5S: rosin ester available from Arizona Chemical Company SEAST (registered trademark) 3: carbon black available from Tokai Carbon Co., Ltd.

Struktol ZP 1014: zinc peroxide (amount of zinc peroxide: 29 mass %) available from Struktol Company

Zinc oxide: “Ginrei R” available from Toho Zinc Co., Ltd.

Sulfur: 5% oil treated sulfur fine powder (200 mesh) available from Tsurumi Chemical Industry Co., Ltd.

Sanceller (registered trademark) TBzTD: tetrabenzylthiuram disulfide available from Sanshin Chemical Industry Co., Ltd.

Nocceler (registered trademark) TOT-N: tetrakis(2-ethylhexyl)thiuram disulfide available from Ouchi Shinko Chemical Industry Co., Ltd.

Nocceler EUR: N, N′-diethylthiourea available from Ouchi Shinko Chemical Industry Co., Ltd.

Microballoons: “Expancel (registered trademark) 909-80DU” (resin capsule encapsulating a hydrocarbon having a low boiling point in a shell formed from a thermoplastic resin, volume average particle size: 18 μm to 24 μm, expansion starting temperature: 120° C. to 130° C.) available from Akzo Nobel Company

The unvulcanized rubber sheet having a fan shape and the cap member were prepared from the outer layer rubber composition. It is noted that the outer layer rubber sheet was formed with a fixed thickness. The unvulcanized rubber sheet having a rectangular shape was prepared from the inner layer rubber composition. It is noted that the inner layer rubber sheet was formed with a thickness gradually becoming thicker from one end toward another end. The inner layer rubber sheet was wound around a mandrel, and then the outer layer rubber sheet was laminated and wound around the inner layer rubber sheet. The mandrel wound with these rubber sheets, and the cap member were charged into a mold having a groove pattern on the cavity surface thereof. A heat treatment was performed at a mold temperature of 160° C. for 15 minutes to obtain golf club grips. In the obtained golf club grips, the cylindrical portion had a thickness of 1.5 mm at the thinnest part (the end on the head side), and a thickness of 6.7 mm at the thickest part (the end on the grip end side). In addition, the surface of the obtained grips was buffed with an abrasive paper (#80).

TABLE 3-1 Grip No. 1 2 3 4 5 Outer layer Rubber composition No. A A A A A Inner layer Rubber composition No. h i j k a NBR proportion (%) 50 30 50 70 0 Unvulcanized surface layer Mooney viscosity 46.2 42.7 41.1 40.4 44.4 properties Vulcanization characteristic Maximum torque value (N · m) 0.547 0.599 0.546 0.550 0.390 Inner layer properties after Material hardness (Shore A) 36 52 41 27 43 vulcanization Elongation at break (%) 623 682 657 702 796 Toluene swollen ratio (%) 176 136 140 148 115 Compression permanent strain 1.6 1.6 1.8 2.0 1.0 Grip evaluation Collapsing resistance 3 3 3 4 4 Weather resistance 3 4 3 3 1

TABLE 3-2 Grip No. 7 8 9 10 11 Outer layer Rubber composition No. A A A A A Inner Rubber composition No. c d e f g layer NBR proportion (%) 100 100 30 50 70 Unvulcanized surface layer Mooney viscosity 51 40.5 40.3 37.9 36.7 properties Vulcanization characteristic Maximum torque value (N · m) 0.588 0.532 0.440 0.405 0.377 Inner layer properties after Material hardness (Shore A) 44 32 48 47 44 vulcanization Elongation at break (%) 753 742 759 791 832 Toluene swollen ratio (%) 258 161 155 240 292 Compression permanent strain 2.6 2.8 1.3 1.4 1.6 Grip evaluation Collapsing resistance 1 1 2 2 3 Weather resistance 4 4 4 3 3

It can be seen from the results shown in Table 3 that the golf club grip according to the present disclosure that comprises a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 Nm or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree, does not collapse and has excellent weather resistance.

This application is based on Japanese patent application No. 2022-070942 filed on Apr. 22, 2022, the content of which is hereby incorporated by reference.

The preferable embodiment (1) according to the present disclosure is a golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 Nm or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree.

The preferable embodiment (2) according to the present disclosure is the golf club grip of the preferable embodiment (1), wherein the cylindrical inner layer is a porous layer.

The preferable embodiment (3) according to the present disclosure is the golf club grip of the preferable embodiment (2), wherein the porous layer has a density in a range from 0.20 g/cm³ to 0.60 g/cm³.

The preferable embodiment (4) according to the present disclosure is the golf club grip according to the preferable embodiment (2) or (3), wherein the cylindrical inner layer is a porous layer obtained by heating the inner layer rubber composition containing microballoons to foam the microballoons.

The preferable embodiment (5) according to the present disclosure is the golf club grip according to any one of the preferable embodiments (1) to (4), wherein the cylindrical inner layer has an elongation at break of 730% or less in a tensile test.

The preferable embodiment (6) according to the present disclosure is the golf club grip according to any one of the preferable embodiments (1) to (5), wherein the cylindrical inner layer has a swollen ratio of 200% or less in a toluene swollen test.

The preferable embodiment (7) according to the present disclosure is the golf club grip according to any one of the preferable embodiments (1) to (6), wherein the acrylonitrile-butadiene based rubber includes an acrylonitrile-butadiene rubber (NBR) and a hydrogenated acrylonitrile-butadiene rubber (HNBR).

The preferable embodiment (8) according to the present disclosure is the golf club grip according to the preferable embodiment (7), wherein an amount of the acrylonitrile-butadiene rubber (NBR) in (A1) the base rubber ranges from 10 mass % to 90 mass %.

The preferable embodiment (9) according to the present disclosure is the golf club grip according to any one of the preferable embodiments (1) to (8), wherein the cylindrical outer layer contains at least one member selected from the group consisting of a carboxyl-modified acrylonitrile-butadiene rubber, a hydrogenated acrylonitrile-butadiene rubber and a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber as (A2) a base rubber.

The preferable embodiment (10) according to the present disclosure is a golf club comprising a shaft, a head provided on one end of the shaft, and a grip provided on another end of the shaft, wherein the grip is the golf club grip according to any one of the preferable embodiments (1) to (9). 

1. A golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 N·m or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree.
 2. The golf club grip according to claim 1, wherein the cylindrical inner layer is a porous layer.
 3. The golf club grip according to claim 2, wherein the porous layer has a density in a range from 0.20 g/cm³ to 0.60 g/cm³.
 4. The golf club grip according to claim 1, wherein the cylindrical inner layer is a porous layer obtained by heating the inner layer rubber composition containing microballoons to foam the microballoons.
 5. The golf club grip according to claim 1, wherein the cylindrical inner layer has an elongation at break of 730% or less in a tensile test.
 6. The golf club grip according to claim 1, wherein the cylindrical inner layer has a swollen ratio of 200% or less in a toluene swollen test.
 7. The golf club grip according to claim 1, wherein the acrylonitrile-butadiene based rubber includes an acrylonitrile-butadiene rubber (NBR) and a hydrogenated acrylonitrile-butadiene rubber (HNBR).
 8. The golf club grip according to claim 7, wherein an amount of the acrylonitrile-butadiene rubber (NBR) in (A1) the base rubber ranges from 10 mass % to 90 mass %.
 9. The golf club grip according to claim 1, wherein the cylindrical outer layer contains at least one member selected from the group consisting of a carboxyl-modified acrylonitrile-butadiene rubber, a hydrogenated acrylonitrile-butadiene rubber and a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber as (A2) a base rubber.
 10. The golf club grip according to claim 1, wherein the maximum torque value ranges from 0.5 N·m to 1.3 N·m.
 11. The golf club grip according to claim 1, wherein the cylindrical inner layer has an elongation at break ranging from 300% to 730% in a tensile test.
 12. The golf club grip according to claim 1, the cylindrical inner layer has a swollen ratio ranging from 100% to 200% in a toluene swollen test.
 13. A golf club comprising a shaft, a head provided on one end of the shaft, and a grip provided on another end of the shaft, wherein the grip is a golf club grip comprising a cylindrical portion having a cylindrical inner layer and a cylindrical outer layer provided outside the cylindrical inner layer, wherein the cylindrical inner layer is formed from an inner layer rubber composition containing an acrylonitrile-butadiene based rubber as (A1) a base rubber, and the inner layer rubber composition has a maximum torque value of 0.5 N·m or more in a vulcanization curve measured at a temperature of 165° C. and an amplitude angle of one degree.
 14. The golf club according to claim 13, wherein the cylindrical inner layer is a porous layer.
 15. The golf club according to claim 13, wherein the cylindrical inner layer has an elongation at break of 730% or less in a tensile test.
 16. The golf club according to claim 13, wherein the cylindrical inner layer has a swollen ratio of 200% or less in a toluene swollen test.
 17. The golf club according to claim 13, wherein the acrylonitrile-butadiene based rubber includes an acrylonitrile-butadiene rubber (NBR) and a hydrogenated acrylonitrile-butadiene rubber (HNBR).
 18. The golf club according to claim 13, wherein an amount of the acrylonitrile-butadiene rubber (NBR) in (A1) the base rubber ranges from 10 mass % to 90 mass %.
 19. The golf club according to claim 13, wherein the cylindrical outer layer contains at least one member selected from the group consisting of a carboxyl-modified acrylonitrile-butadiene rubber, a hydrogenated acrylonitrile-butadiene rubber and a carboxyl-modified hydrogenated acrylonitrile-butadiene rubber as (A2) a base rubber.
 20. The golf club according to claim 13, wherein the maximum torque value ranges from 0.5 N·m to 1.3 N·m, and the cylindrical inner layer has an elongation at break ranging from 300% to 730% in a tensile test and has a swollen ratio ranging from 100% to 200% in a toluene swollen test. 